It is known to make dianhydrides from maleic anhydride as is taught in commonly-assigned Ser. No. 294,322, and Ser. No. 386,891, which are hereby incorporated by reference. It is also known to make polyimides from dianhydrides and aromatic amines. This is disclosed in U.S. Pat. No. 3,179,634 (1965). British Patent Specification No. 570,858 discloses various processes for making fiber-forming polymers.
In reviewing these references, it is clear that the reaction of anhydrides prepared from maleic anhydride compounds with olefins in a mole ratio of 2:1, two moles of anhydride to one mole of olefin, to prepare dianhydrides has not been contemplated in the prior art. Also, the prior art has not contemplated the novel dianhydrides prepared by photocycloaddition of maleic anhydride compounds to at least one cyclic diolefin of the structural formula ##STR3## wherein R.sup.1 and R.sup.2 are individually selected from the group consisting of alkylene moieties of from 1 to 10 carbon atoms and aralkylene moieties of from 8 to 20 carbon atoms or alpha, omega-diolefins of the structure (CH.sub.2 .dbd.CH.sub.2 CH.sub.2).sub.2 R' wherein R' is selected from the group consisting of alkylene groups of from 0 to 20 carbon atoms, aralkylene groups of from 8 to 20 carbon atoms and aryl groups of 6 to 20 carbon atoms with the provision that hydrocarbon linkages of said moieties can contain stable linkages selected from the group consisting of --O--, ##STR4## --SO--, SO.sub.2 and --S-- radicals. The maleic anhydride compound is selected from the group consisting of maleic anhydride compounds of the structural formula ##STR5## wherein R is individually selected from the group consisting of alkyl moieties of from 1 to 10 carbon atoms and alkylene moieties of from 2 to 20 carbon atoms linked together to form a ring. Examples are dimethyl maleic anhydride and 1-cyclohexene-1,2-dicarboxylic acid anhydride, a compound made by isomerizing the Diels-Alder adduct of butadiene and maleic anhydride (M. E. Bailey and E. D. Amstutz, JACS, 78, 3828 (1956)).
The general object of this invention is to provide novel dianhydrides prepared from maleic anhydride compounds with diolefins in a mole ratio of 2:1 and to provide novel polyimides based on these novel dianhydrides. A more specific object of this invention is to provide novel dianhydrides from dimethyl maleic anhydride designated as compound (1), or 1-cyclohexene-1,2-dicarboxylic anhydride, designated as compound (2) and diolefins selected from the group consisting of 1,5-cyclooctadiene, 1,5-hexadiene, and 1,7-octadiene. Another more specific object of this invention is also to provide novel polyimides prepared from the said novel dianhydrides. Another specific object of this invention is to provide a simple procedure for the preparation of these dianhydrides by the photocycloaddition of the maleic anhydride compounds to the respective diolefins.